Revert Back To The Old Google Sites User Interface
So here is how to disable the new user interface.
Ok > go to sites.google.com (or go to your google site) and log in with your google account > click on the 'user settings' link which is located under the cog like settings icon in the top right of your browser's page.
Uncheck the box beside 'use the new look'
Remember to save your changes then you are done!